(1) For a vibratory hammer to be suitable for a particular application, the dynamic force

should suit the equation

Fdyn $ i ($o@Rso+$i@Rsi+$t@Rt)/R

where

Fdyn

=

dynamic force of vibrator, tons

=

beta factor for soil resistance (general)

$

=

beta factor for soil resistance (outside shaft)

$i

=

beta factor for soil resistance (inside shaft)

$o

=

beta factor for soil resistance (toe)

$t

Rsi

=

inside pile shaft soil resistance, tons

Rso

=

outside pile shaft soil resistance, tons

Rt

=

pile toe soil resistance, kN.

=

pile factor (0.8 for concrete piling and 1 for all

Q

other piling.)

=

soil resilience coefficient (should be between 0.6

i

and 0.8 for vibration frequencies between 5 and

10 Hz and 1 for all other frequencies.)

Suggested values for $ are given in table 2-2. The toe resistance and the outside and

inside (where applicable with open-end pipe and cylinder pile) shaft resistance should be

computed using methods similar to those employed for impact hammers. For extraction,

this formula is altered to read

Fdyn $ i ($o Rso+$i Rsi+$t Rt)/R-Fext

where

Fext

=

extraction force of crane, tons

(2) Once this is known, a possible vibratory hammer for the job should be selected

based on minimum permissible dynamic force in tons. The parameter of dynamic mass

(the dynamic mass includes any mass of the vibrator not dampened from vibration, the

clamp and any mass of the pile) should be noted, along with the frequency and eccentric

moment of the machine.

(3) Next the basic parameters of the vibratory hammer/pile system must be checked.

The first is the peak acceleration, whose value is computed using the equation

n = 2000 Fdyn / Wdyn

where

n

=

peak acceleration, g's

Mdyn =

dynamic mass of system, pounds

Minimum values for this acceleration are given in table 2-3.

Figure 2-2b. Method for Sizing Vibratory Hammers, English Units.

2-11

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